Peplexicon Lab · Start here

What is a peptide, really?

You’ve seen the word on weight-loss drugs, supplements, and skin creams. Here’s what peptides are, how they’re made, how they work in the body, and how anyone knows if they help. Six short stops. No science background needed.

Choose your depth

The essentials in plain language. Your reading level. The same underlying facts.

Start the tour Skip to: does it work?

Every picture here is simplified, and says so. Want more detail? Switch to Learning or Scientific at any time. The facts stay the same.

One peptide, six benches.The open ring: questions still being studied.

01Build · What a peptide is

Beads on a string.

A peptide is a short chain of building blocks called amino acids. There are 20 kinds, and their order decides what the peptide does—like letters spelling a word. Pick a real one, or build your own.

Chain builderA simplified picture · not to scale

Setting up the 3D bench…

The gold bridge locks block 1 to block 6, closing a ring.

Try a real one

Or tap building blocks to make your own chain. The colours group blocks that behave alike.

Water-avoiding

Ring-shaped

Water-loving

Positive

Negative

Shape-setters

Building blocks: 98 links between them
Kind: Peptideup to 40 blocks
Electric charge: Slightly positivein the body
Mixes with water: Fairly well

02Discover · How peptides are found

Where do new peptides come from?

Some are copied from our own bodies. Some come from animal venom. Some are improved versions of natural ones. And some are found by testing billions of random chains to see which one grabs a target. Try that last one below.

01
Copied from the body
Many medicines start as hormones our bodies already make, like insulin.
Insulin, 1921
02
Found in nature
Animal venoms are full of peptides. A Gila monster’s venom led to a diabetes drug; a sea snail’s venom led to a pain medicine.
Exendin-4, 1992
03
Improved by chemists
Scientists change a few parts of a natural peptide so it lasts longer in the body.
Semaglutide, 2017
04
Found by searching billions
Make billions of random peptides and keep the few that stick to a target. Try it below.
Phage display, 1985

Fishing for a matchA simulation · each dot is one virus

Good match
Weak match
No match
Fake match (sticks to plastic)

Rinses: 0of up to 5
Good matches: 0.4%of the dots
Fake matches: 1.1%stuck to plastic

Good matches after each rinseDark blue is good matches. The bar fills with them as you rinse.

The winners so farScientists read the genes of the survivors to learn which peptides they carry. Each letter is one building block.

Peptide	How it sticks	Share
`GRINFKG`	No match	0.13%
`HWINRKA`	No match	0.13%
`QAFVIDN`	No match	0.13%
`TEWSAVQ`	No match	0.13%
`MWHGNMF`	No match	0.13%

These sequences are made up for this simulation.

About 100 years of peptide medicine

How we got here

1921Found in the body
Insulin is isolated
Banting and Best extract insulin from the pancreas. A 14-year-old is treated in January 1922—the first peptide-hormone therapy.
Source
1953Method
Oxytocin is made in a lab
Vincent du Vigneaud synthesizes oxytocin, the first polypeptide hormone built from scratch.
Source
1955Method
A protein gets a sequence
Frederick Sanger completes the amino-acid order of insulin, proving each protein has a defined sequence.
Source
1963Method
Chains anchored to beads
Bruce Merrifield builds peptides on a solid resin bead, turning weeks of work into repeatable cycles.
Source
1982Medicine
Cells become factories
Human insulin made by engineered bacteria (Humulin) is approved: the first medicine made with recombinant DNA.
Source
1985Method
Libraries of billions
George Smith shows viruses can display peptides on their surface, making it possible to screen enormous libraries.
Source
1992Found in nature
A lizard’s venom
Researchers isolate exendin-4 from Gila monster venom. It acts on the GLP-1 receptor.
Source
2004Medicine
A cone snail’s toxin
Ziconotide, based on a peptide from cone snail venom, is approved for severe chronic pain.
Source
2005Medicine
Exenatide approved
A synthetic copy of exendin-4 becomes the first GLP-1 receptor agonist approved in the US.
Source
2017Medicine
Semaglutide approved
An engineered GLP-1 lasting about a week is approved as a once-weekly injection.
Source
2020Regulation
The 40–amino acid line
Medicines longer than 40 amino acids, including insulin, transition to regulation as biologics in the US.
Source

03Make · How peptides are made

Built one piece at a time.

A machine builds a peptide by adding one building block at a time, to millions of chains at once. Each step works almost every time—but “almost” adds up. Press Run and watch.

Peptide builderShows 42 of the millions of chains on a real bead

Uncap
Add a block
Rinse

How often each step works

Steps: 8to add 8 blocks
Perfect chains: 92%no mistakes
With a mistake: 8%missed at least one step

Longer chains, more mistakesShare of chains with no mistakes, by length. Small misses add up.

Two ways to make a peptide

Chemistry

Made by a machine

What you just watched. Good for short chains, and chemists can use building blocks nature doesn’t.

Biology

Grown by yeast or bacteria

Scientists give microbes the instructions (a gene), and the microbes build the chain for them. Longer chains, like insulin, are usually made this way.

Human insulin made by bacteria was approved in 1982—the first medicine made this way.
Ozempic’s label says the main chain of semaglutide is made by yeast.

Sources

04Test · How a batch is checked

Is it really what the label says?

Before a medicine can be sold, labs check that it’s the right molecule, that it’s pure, and that it’s free of germs. Here are two of those checks, run on the batch you just made.

Purity checkSimplified · the tall peak is your peptide

The real thing: 93%raw batch
Mistakes: 7%chains missing a block

Weight checkIs it the right molecule?

Expected weight of Oxytocin: 1,007.2
Measured: 1,007.2
Result: Right molecule

A machine called a mass spectrometer weighs molecules. A chain missing one block would weigh less, so this check catches many mistakes. Weights are in daltons, a unit sized for molecules.

The checks a medicine must pass

Before a batch of an approved medicine can be sold, it has to pass every check on a list that regulators have reviewed. Here are four of them.

Is it the right molecule?
Weigh the molecules and compare with the expected weight.
Checked above: yes
How pure is it?
Sort the batch and measure how much is the real thing.
Checked above: 93%
Is it free of bacterial toxins?
A test that detects toxins from bacteria, which can cause fever if injected.
Not shown here
Is it free of germs?
Grow samples to check that nothing living is in a product meant for injection.
Not shown here

A clean test result tells you what’s in the vial—not whether it works or is safe for you. That takes the studies at the last stop. Products sold “for research use only” aren’t approved for people and don’t have to pass these checks.

05Act · How peptides work in the body

A key, a lock, and a clock.

A peptide works like a key. It fits a lock on a cell, called a receptor, and tells the cell to do something. But the body clears peptides out fast, so much of the cleverness in modern peptide medicines is making them last.

Locks on a cellA simplified picture

How much peptide

The key

Locks filled: 50%4 of 8 shown
Switched on: 50%sending a signal

How long it lastsSimplified · one dose · not a dosing guide

Time since the dose

Half gone in: ~1 week
Still in the blood: 91%after 24 h
Vs. natural GLP-1: 5,040×longer lasting
Protected from: the scissors · the kidneys

06Prove · How we learn if it helps

How do we know if it works?

Something that works in a dish or in mice may not work in people. The only way to know is to test it in people, step by step, with a fair comparison. Try running a fair test yourself.

The steps to proofBased on FDA’s guide for patients

Big tests (Phase 3)

Does it work better than a dummy treatment or current care?

Who or what is tested: 300 to 3,000 people with the condition
It can show: Confirm the benefit and the common side effects.
It can’t show: Catch very rare or very long-term harms.
On Peplexicon, labelled as: Fair tests in people

About 28 in 100 medicines at this step make it to the next one, by FDA’s estimate.

Of every 100 medicines tested in people

Start tests in people100

Reach medium tests70

Reach big tests23

Reach FDA reviewabout 6

Most never make it. And many more fail before they’re ever tested in people.

Semaglutide passed every step, including big tests in thousands of people, and was approved in 2017. See what the research found →

BPC-157 has mostly been tested in animals. It isn’t FDA-approved, and there’s no reliable evidence yet that it helps people.

FDA: The drug development process, Step 3: clinical research ↗

Fair-test simulatorSimulated people · not real data

People in each group

The truth

Show the truth on the chart

Result: —run a test
Looked like it worked: —tests so far
Chance to spot it: 20%for a test this size

End of the tour

Now you know what to ask.

When you read about any peptide—here or anywhere else—ask three questions. Was it tested in people, or only in animals? Was it a fair test with a comparison group? Is it approved, or sold “for research use only”?

Look up a peptide How we check the evidence

What this tour can’t tell you

These are simple pictures. Real molecules are too small to see, and real labs are messier.
Nothing here predicts what will happen to you. Bodies differ, and so do products.
This is not medical advice. Talk to a doctor or pharmacist about any medicine, including peptides.

Every source used in the lab (33)

What is a peptide, really?

Copied from the body

Found in nature

Improved by chemists

Found by searching billions

How we got here

Insulin is isolated

Oxytocin is made in a lab

A protein gets a sequence

Chains anchored to beads

Cells become factories

Libraries of billions

A lizard’s venom

A cone snail’s toxin

Exenatide approved